Carsten Detlefs

An X-ray beam can peer inside an opaque piece of metal and show where cracks or stresses are hiding. But to see such defects, the beam must be focused into a very narrow pencil, just as sunlight is focused by a magnifying glass into a hot spot. In an X-ray microscope, the lens plays the role of the magnifying glass.

Inside a piece of aluminum, atoms are arranged in neat rows, like bricks in a wall. But sometimes a row ends before reaching the edge, and a "step" appears in the crystal, which physicists call a dislocation. These defects determine how strong, ductile, and how a metal behaves under load.

In a chunk of the meteorite EET 87720, found in Antarctic ice, lies a pink grain of sand. It's spinel, a mineral almost never seen in ureilites, and here it grew to half a millimeter. Such a find is like a time capsule from an early melt: it solidified when the parent body was just beginning to cool.